Solid electrolytic capacitor with stable electrical properties at high temperatures

ABSTRACT

A solid electrolytic capacitor is provided that contains a casing material that encapsulates the capacitor element. The casing material is formed from a curable resinous matrix that has a coefficient of thermal expansion of about 42 ppm/° C. or less at a temperature above the glass transition temperature of the resinous matrix. Further, the capacitor exhibits an initial equivalence series resistance of about 200 mohms or less as determined at an operating frequency of 100 kHz and temperature of 23° C., and the ratio of the equivalence series resistance of the capacitor after being exposed to a temperature of 125° C. for 560 hours to the initial equivalence series resistance of the capacitor is about 2.0 or less.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims filing benefit of U.S. Provisional PatentApplication Ser. No. 62/687,961 having a filing date of Jun. 21, 2018,which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Electrolytic capacitors (e.g., tantalum capacitors) are increasinglybeing used in the design of circuits due to their volumetric efficiency,reliability, and process compatibility. For example, one type ofcapacitor that has been developed is a solid electrolytic capacitor thatincludes a tantalum anode, dielectric layer, and conductive polymersolid electrolyte. To help protect the capacitor from the exteriorenvironment and provide it with good mechanical stability, the capacitorelement is also encapsulated with a casing material (e.g., epoxy resin)so that a portion of the anode and cathode terminations remain exposedfor mounting to a surface. Unfortunately, it has been discovered thathigh temperatures that are often used during manufacture of thecapacitor (e.g., reflow) can cause residual moisture to vaporize assteam, which may exit the case with considerable force and causemicro-cracks to form in the casing material. These micro-cracks can leadto delamination of the casing material from the capacitor element andalso a rapid deterioration of the electrical properties, particularlywhen the capacitor is exposed to high temperatures. As such, a needexists for an improved solid electrolytic capacitor that exhibitsrelatively stable electrical properties at high temperatures.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a solidelectrolytic capacitor is disclosed that comprises a capacitor elementthat contains a sintered porous anode body, a dielectric that overliesthe anode body, and a solid electrolyte that overlies the dielectric; ananode lead extending from a surface of the capacitor element; an anodetermination that is in electrical connection with the anode lead; acathode termination that is in electrical connection with the solidelectrolyte; and a casing material that encapsulates the capacitorelement and anode lead is provided. The casing material is formed from acurable resinous matrix that has a coefficient of thermal expansion ofabout 42 ppm/° C. or less at a temperature above the glass transitiontemperature of the resinous matrix. Further, the capacitor exhibits aninitial equivalence series resistance of about 200 mohms or less asdetermined at an operating frequency of 100 kHz and temperature of 23°C., and the ratio of the equivalence series resistance of the capacitorafter being exposed to a temperature of 125° C. for 560 hours to theinitial equivalence series resistance of the capacitor is about 2.0 orless.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWING

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended drawing in which:

FIG. 1 is a schematic illustration of one embodiment of a solidelectrolytic capacitor that may be formed in accordance with the presentinvention.

Repeat use of references characters in the present specification anddrawing is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstruction.

Generally speaking, the present invention is directed to a solidelectrolytic capacitor that contains a capacitor element including aporous anode body, dielectric overlying the anode body, and solidelectrolyte overlying the dielectric. An anode lead extends from theanode body and is in electrical contact with an anode termination. Acathode termination is likewise in electrical contact with the solidelectrolyte. Further, a casing material encapsulates the capacitorelement and anode lead and leaves exposed at least a portion of theanode termination and cathode termination for external contact. Thecasing material is formed from a curable resinous matrix that has arelatively low coefficient of thermal expansion. For example, theresinous matrix typically has a coefficient of thermal expansion ofabout 42 ppm/° C. or less, in some embodiments about 40 ppm/° C. orless, and in some embodiments, from about 20° ppm/C to about 38 ppm/° C.at a temperature above the glass transition temperature of the resinousmatrix. Likewise, the resinous matrix also typically has a coefficientof thermal expansion of about 11 ppm/° C. or less, in some embodimentsabout 10 ppm/° C. or less, and in some embodiments, from about 1 toabout 9 ppm/° C. at a temperature below the glass transition temperatureof the resinous matrix. The glass transition temperature of the resinousmatrix may, for example, range from about 50° C. to about 180° C., insome embodiments about 60° C. to about 160° C., and in some embodiments,from about 80° C. to about 150° C. The coefficient of thermal expansionand glass transition temperature may be determined using techniquesknown in the art, such as in accordance with thermal mechanical analysis(“TMA”) in accordance with ISO 11359-2:1999. Without intending to belimited by theory, it is believed that the use of a resinous matrix withsuch a low coefficient of thermal expansion can result in a casingmaterial that is less likely to delaminate from the capacitor elementwhen exposed to the high temperatures often experienced duringmanufacturing of the capacitor (e.g., reflow).

Through selective control over the particular nature of the casingmaterial and interfacial coating, the resulting capacitor is may beresistant to delamination during manufacturing and can thus exhibitexcellent electrical properties. For example, the capacitor may exhibita relatively low equivalence series resistance (“ESR”), such as about200 mohms, in some embodiments less than about 150 mohms, in someembodiments from about 0.1 to about 125 mohms, and in some embodiments,from about 1 to about 100 mohms, measured at an operating frequency of100 kHz and temperature of 23° C. The capacitor may also exhibit a drycapacitance of about 30 nanoFarads per square centimeter (“nF/cm²”) ormore, in some embodiments about 100 nF/cm² or more, in some embodimentsfrom about 200 to about 3,000 nF/cm², and in some embodiments, fromabout 400 to about 2,000 nF/cm², measured at a frequency of 120 Hz attemperature of 23° C.

Notably, such electrical properties (e.g., ESR and/or capacitance) canstill remain stable even at high temperatures. For example, thecapacitor may exhibit an ESR and/or capacitance value within the rangesnoted above even after being exposed to a temperature of from about 80°C. or more, in some embodiments from about 100° C. to about 150° C., andin some embodiments, from about 105° C. to about 130° C. (e.g., 105° C.or 125° C.) for a substantial period of time, such as for about 560hours or more, in some embodiments from about 700 hours to about 2,000hours, and in some embodiments, from about 900 hours to about 1,500hours (e.g., 240, 420, 560, 750, 1,000, or 1,250 hours). In oneembodiment, for example, the ratio of the ESR and/or capacitance valueof the capacitor after being exposed to the high temperature (e.g., 125°C.) for 560, 750, 1,000, and/or 1,250 hours to the initial ESR and/orcapacitance value of the capacitor (e.g., at 23° C.) is about 2.0 orless, in some embodiments about 1.5 or less, and in some embodiments,from 1.0 to about 1.3. The capacitor may also exhibit an ESR and/orcapacitance value within the ranges noted above after being exposed to ahigh relative humidity level, either at room temperature or a hightemperature (e.g., 85° C. or 125° C.). Such high relative humiditylevels may, for instance, be about 40% or more, in some embodimentsabout 45% or more, in some embodiments about 50% or more, and in someembodiments, about 70% or more (e.g., about 85% to 100%) for asubstantial period of time as noted above. Relative humidity may, forinstance, be determined in accordance with ASTM E337-02, Method A(2007). In one embodiment, for example, the ratio of the ESR and/orcapacitance value of the capacitor after being exposed to high humidity(e.g., 85%) for 240 hours to the initial ESR and/or capacitance value ofthe capacitor is about 2.0 or less, in some embodiments about 1.5 orless, and in some embodiments, from 1.0 to about 1.3.

In addition, the capacitor may also exhibit a DCL of only about 50microamps (“μA”) or less, in some embodiments about 40 μA or less, insome embodiments about 20 μA or less, and in some embodiments, fromabout 0.1 to about 10 μA. Further, the capacitor may exhibit a highpercentage of its wet capacitance, which enables it to have only a smallcapacitance loss and/or fluctuation in the presence of atmospherehumidity. This performance characteristic is quantified by the“capacitance recovery”, which is determined by the equation:Recovery=(Dry Capacitance/Wet Capacitance)×100

The capacitor may exhibit a capacitance recovery of about 50% or more,in some embodiments about 60% or more, in some embodiments about 70% ormore, and in some embodiments, from about 80% to 100%.

Various embodiments of the capacitor will now be described in moredetail.

I. Capacitor Element

A. Anode Body

The capacitor element includes an anode that contains a dielectricformed on a sintered porous body. The porous anode body may be formedfrom a powder that contains a valve metal (i.e., metal that is capableof oxidation) or valve metal-based compound, such as tantalum, niobium,aluminum, hafnium, titanium, alloys thereof, oxides thereof, nitridesthereof, and so forth. The powder is typically formed from a reductionprocess in which a tantalum salt (e.g., potassium fluorotantalate(K₂TaF₇), sodium fluorotantalate (Na₂TaF₇), tantalum pentachloride(TaCl₅), etc.) is reacted with a reducing agent. The reducing agent maybe provided in the form of a liquid, gas (e.g., hydrogen), or solid,such as a metal (e.g., sodium), metal alloy, or metal salt. In oneembodiment, for instance, a tantalum salt (e.g., TaCl₅) may be heated ata temperature of from about 900° C. to about 2,000° C., in someembodiments from about 1,000° C. to about 1,800° C., and in someembodiments, from about 1,100° C. to about 1,600° C., to form a vaporthat can be reduced in the presence of a gaseous reducing agent (e.g.,hydrogen). Additional details of such a reduction reaction may bedescribed in WO 2014/199480 to Maeshima, et al. After the reduction, theproduct may be cooled, crushed, and washed to form a powder.

The specific charge of the powder typically varies from about 2,000 toabout 600,000 microFarads*Volts per gram (“μF*V/g”) depending on thedesired application. For instance, in certain embodiments, a high chargepowder may be employed that has a specific charge of from about 100,000to about 550,000 μF*V/g, in some embodiments from about 120,000 to about500,000 μF*V/g, and in some embodiments, from about 150,000 to about400,000 μF*V/g. In other embodiments, a low charge powder may beemployed that has a specific charge of from about 2,000 to about 100,000μF*V/g, in some embodiments from about 5,000 to about 80,000 μF*V/g, andin some embodiments, from about 10,000 to about 70,000 μF*V/g. As isknown in the art, the specific charge may be determined by multiplyingcapacitance by the anodizing voltage employed, and then dividing thisproduct by the weight of the anodized electrode body.

The powder may be a free-flowing, finely divided powder that containsprimary particles. The primary particles of the powder generally have amedian size (D50) of from about 5 to about 500 nanometers, in someembodiments from about 10 to about 400 nanometers, and in someembodiments, from about 20 to about 250 nanometers, such as determinedusing a laser particle size distribution analyzer made by BECKMANCOULTER Corporation (e.g., LS-230), optionally after subjecting theparticles to an ultrasonic wave vibration of 70 seconds. The primaryparticles typically have a three-dimensional granular shape (e.g.,nodular or angular). Such particles typically have a relatively low“aspect ratio”, which is the average diameter or width of the particlesdivided by the average thickness (“D/T”). For example, the aspect ratioof the particles may be about 4 or less, in some embodiments about 3 orless, and in some embodiments, from about 1 to about 2. In addition toprimary particles, the powder may also contain other types of particles,such as secondary particles formed by aggregating (or agglomerating) theprimary particles. Such secondary particles may have a median size (D50)of from about 1 to about 500 micrometers, and in some embodiments, fromabout 10 to about 250 micrometers.

Agglomeration of the particles may occur by heating the particles and/orthrough the use of a binder. For example, agglomeration may occur at atemperature of from about 0° C. to about 40° C., in some embodimentsfrom about 5° C. to about 35° C., and in some embodiments, from about15° C. to about 30° C. Suitable binders may likewise include, forinstance, poly(vinyl butyral); poly(vinyl acetate); poly(vinyl alcohol);poly(vinyl pyrollidone); cellulosic polymers, such ascarboxymethylcellulose, methyl cellulose, ethyl cellulose, hydroxyethylcellulose, and methylhydroxyethyl cellulose; atactic polypropylene,polyethylene; polyethylene glycol (e.g., Carbowax from Dow ChemicalCo.); polystyrene, poly(butadiene/styrene); polyamides, polyimides, andpolyacrylamides, high molecular weight polyethers; copolymers ofethylene oxide and propylene oxide; fluoropolymers, such aspolytetrafluoroethylene, polyvinylidene fluoride, and fluoro-olefincopolymers; acrylic polymers, such as sodium polyacrylate, poly(loweralkyl acrylates), poly(lower alkyl methacrylates) and copolymers oflower alkyl acrylates and methacrylates; and fatty acids and waxes, suchas stearic and other soapy fatty acids, vegetable wax, microwaxes(purified paraffins), etc.

The resulting powder may be compacted to form a pellet using anyconventional powder press device. For example, a press mold may beemployed that is a single station compaction press containing a die andone or multiple punches. Alternatively, anvil-type compaction pressmolds may be used that use only a die and single lower punch. Singlestation compaction press molds are available in several basic types,such as cam, toggle/knuckle and eccentric/crank presses with varyingcapabilities, such as single action, double action, floating die,movable platen, opposed ram, screw, impact, hot pressing, coining orsizing. The powder may be compacted around an anode lead, which may bein the form of a wire, sheet, etc. The lead may extend in a longitudinaldirection from the anode body and may be formed from any electricallyconductive material, such as tantalum, niobium, aluminum, hafnium,titanium, etc., as well as electrically conductive oxides and/ornitrides of thereof. Connection of the lead may also be accomplishedusing other known techniques, such as by welding the lead to the body orembedding it within the anode body during formation (e.g., prior tocompaction and/or sintering).

Any binder may be removed after pressing by heating the pellet undervacuum at a certain temperature (e.g., from about 150° C. to about 500°C.) for several minutes. Alternatively, the binder may also be removedby contacting the pellet with an aqueous solution, such as described inU.S. Pat. No. 6,197,252 to Bishop, et al. Thereafter, the pellet issintered to form a porous, integral mass. The pellet is typicallysintered at a temperature of from about 700° C. to about 1800° C., insome embodiments from about 800° C. to about 1700° C., and in someembodiments, from about 900° C. to about 1400° C., for a time of fromabout 5 minutes to about 100 minutes, and in some embodiments, fromabout 8 minutes to about 15 minutes. This may occur in one or moresteps. If desired, sintering may occur in an atmosphere that limits thetransfer of oxygen atoms to the anode. For example, sintering may occurin a reducing atmosphere, such as in a vacuum, inert gas, hydrogen, etc.The reducing atmosphere may be at a pressure of from about 10 Torr toabout 2000 Torr, in some embodiments from about 100 Torr to about 1000Torr, and in some embodiments, from about 100 Torr to about 930 Torr.Mixtures of hydrogen and other gases (e.g., argon or nitrogen) may alsobe employed.

B. Dielectric

The anode is also coated with a dielectric. The dielectric may be formedby anodically oxidizing (“anodizing”) the sintered anode so that adielectric layer is formed over and/or within the anode. For example, atantalum (Ta) anode may be anodized to tantalum pentoxide (Ta₂O₅).Typically, anodization is performed by initially applying a solution tothe anode, such as by dipping anode into the electrolyte. A solvent isgenerally employed, such as water (e.g., deionized water). To enhanceionic conductivity, a compound may be employed that is capable ofdissociating in the solvent to form ions. Examples of such compoundsinclude, for instance, acids, such as described below with respect tothe electrolyte. For example, an acid (e.g., phosphoric acid) mayconstitute from about 0.01 wt. % to about 5 wt. %, in some embodimentsfrom about 0.05 wt. % to about 0.8 wt. %, and in some embodiments, fromabout 0.1 wt. % to about 0.5 wt. % of the anodizing solution. Ifdesired, blends of acids may also be employed.

A current is passed through the anodizing solution to form thedielectric layer. The value of the formation voltage manages thethickness of the dielectric layer. For example, the power supply may beinitially set up at a galvanostatic mode until the required voltage isreached. Thereafter, the power supply may be switched to apotentiostatic mode to ensure that the desired dielectric thickness isformed over the entire surface of the anode. Of course, other knownmethods may also be employed, such as pulse or step potentiostaticmethods. The voltage at which anodic oxidation occurs typically rangesfrom about 4 to about 250 V, and in some embodiments, from about 5 toabout 200 V, and in some embodiments, from about 10 to about 150 V.During oxidation, the anodizing solution can be kept at an elevatedtemperature, such as about 30° C. or more, in some embodiments fromabout 40° C. to about 200° C., and in some embodiments, from about 50°C. to about 100° C. Anodic oxidation can also be done at ambienttemperature or lower. The resulting dielectric layer may be formed on asurface of the anode and within its pores.

Although not required, in certain embodiments, the dielectric layer maypossess a differential thickness throughout the anode in that itpossesses a first portion that overlies an external surface of the anodeand a second portion that overlies an interior surface of the anode. Insuch embodiments, the first portion is selectively formed so that itsthickness is greater than that of the second portion. It should beunderstood, however, that the thickness of the dielectric layer need notbe uniform within a particular region. Certain portions of thedielectric layer adjacent to the external surface may, for example,actually be thinner than certain portions of the layer at the interiorsurface, and vice versa. Nevertheless, the dielectric layer may beformed such that at least a portion of the layer at the external surfacehas a greater thickness than at least a portion at the interior surface.Although the exact difference in these thicknesses may vary depending onthe particular application, the ratio of the thickness of the firstportion to the thickness of the second portion is typically from about1.2 to about 40, in some embodiments from about 1.5 to about 25, and insome embodiments, from about 2 to about 20.

To form a dielectric layer having a differential thickness, amulti-stage process is generally employed. In each stage of the process,the sintered anode is anodically oxidized (“anodized”) to form adielectric layer (e.g., tantalum pentoxide). During the first stage ofanodization, a relatively small forming voltage is typically employed toensure that the desired dielectric thickness is achieved for the innerregion, such as forming voltages ranging from about 1 to about 90 volts,in some embodiments from about 2 to about 50 volts, and in someembodiments, from about 5 to about 20 volts. Thereafter, the sinteredbody may then be anodically oxidized in a second stage of the process toincrease the thickness of the dielectric to the desired level. This isgenerally accomplished by anodizing in an electrolyte at a highervoltage than employed during the first stage, such as at formingvoltages ranging from about 50 to about 350 volts, in some embodimentsfrom about 60 to about 300 volts, and in some embodiments, from about 70to about 200 volts. During the first and/or second stages, theelectrolyte may be kept at a temperature within the range of from about15° C. to about 95° C., in some embodiments from about 20° C. to about90° C., and in some embodiments, from about 25° C. to about 85° C.

The electrolytes employed during the first and second stages of theanodization process may be the same or different. Typically, however, itis desired to employ different solutions to help better facilitate theattainment of a higher thickness at the outer portions of the dielectriclayer. For example, it may be desired that the electrolyte employed inthe second stage has a lower ionic conductivity than the electrolyteemployed in the first stage to prevent a significant amount of oxidefilm from forming on the internal surface of anode. In this regard, theelectrolyte employed during the first stage may contain an acidiccompound, such as nitric acid, sulfuric acid, phosphoric acid,polyphosphoric acid, boric acid, boronic acid, etc. Such an electrolytemay have an electrical conductivity of from about 0.1 to about 100mS/cm, in some embodiments from about 0.2 to about 20 mS/cm, and in someembodiments, from about 1 to about 10 mS/cm, determined at a temperatureof 25° C. The electrolyte employed during the second stage typicallycontains a salt of a weak acid so that the hydronium ion concentrationincreases in the pores as a result of charge passage therein. Iontransport or diffusion is such that the weak acid anion moves into thepores as necessary to balance the electrical charges. As a result, theconcentration of the principal conducting species (hydronium ion) isreduced in the establishment of equilibrium between the hydronium ion,acid anion, and undissociated acid, thus forms a poorer-conductingspecies. The reduction in the concentration of the conducting speciesresults in a relatively high voltage drop in the electrolyte, whichhinders further anodization in the interior while a thicker oxide layer,is being built up on the outside to a higher formation voltage in theregion of continued high conductivity. Suitable weak acid salts mayinclude, for instance, ammonium or alkali metal salts (e.g., sodium,potassium, etc.) of boric acid, boronic acid, acetic acid, oxalic acid,lactic acid, adipic acid, etc. Particularly suitable salts includesodium tetraborate and ammonium pentaborate. Such electrolytes typicallyhave an electrical conductivity of from about 0.1 to about 20 mS/cm, insome embodiments from about 0.5 to about 10 mS/cm, and in someembodiments, from about 1 to about 5 mS/cm, determined at a temperatureof 25° C.

If desired, each stage of anodization may be repeated for one or morecycles to achieve the desired dielectric thickness. Furthermore, theanode may also be rinsed or washed with another solvent (e.g., water)after the first and/or second stages to remove the electrolyte.

C. Solid Electrolyte

A solid electrolyte overlies the dielectric and generally functions asthe cathode for the capacitor. The solid electrolyte may includematerials as is known in the art, such as conductive polymers (e.g.,polypyrroles, polythiophenes, polyanilines, etc.), manganese dioxide,and so forth. In one embodiment, for example, the solid electrolytecontains one or more layers containing extrinsically and/orintrinsically conductive polymer particles. One benefit of employingsuch particles is that they can minimize the presence of ionic species(e.g., Fe²⁺ or Fe³⁺) produced during conventional in situ polymerizationprocesses, which can cause dielectric breakdown under high electricfield due to ionic migration. Thus, by applying the conductive polymeras pre-polymerized particles rather through in situ polymerization, theresulting capacitor may exhibit a relatively high “breakdown voltage.”If desired, the solid electrolyte may be formed from one or multiplelayers. When multiple layers are employed, it is possible that one ormore of the layers includes a conductive polymer formed by in situpolymerization. However, when it is desired to achieve very highbreakdown voltages, the solid electrolyte may desirably be formedprimarily from the conductive particles described above, such that it isgenerally free of conductive polymers formed via in situ polymerization.Regardless of the number of layers employed, the resulting solidelectrolyte typically has a total a thickness of from about 1 micrometer(μm) to about 200 μm, in some embodiments from about 2 μm to about 50μm, and in some embodiments, from about 5 μm to about 30 μm.

Thiophene polymers are particularly suitable for use in the solidelectrolyte. In certain embodiments, for instance, an “extrinsically”conductive thiophene polymer may be employed in the solid electrolytethat has repeating units of the following formula (I):

wherein,

R₇ is a linear or branched, C₁ to C₁₈ alkyl radical (e.g., methyl,ethyl, n- or iso-propyl, n-, iso-, sec- or tert-butyl, n-pentyl,1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1-ethylpropyl,1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, n-hexyl,n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl,n-tridecyl, n-tetradecyl, n-hexadecyl, n-octadecyl, etc.); C₅ to C₁₂cycloalkyl radical (e.g., cyclopentyl, cyclohexyl, cycloheptyl,cyclooctyl, cyclononyl, cyclodecyl, etc.); C₆ to C₁₄ aryl radical (e.g.,phenyl, naphthyl, etc.); C₇ to C₁₈ aralkyl radical (e.g., benzyl, o-,m-, p-tolyl, 2,3-, 2,4-, 2,5-, 2-6, 3-4-, 3,5-xylyl, mesityl, etc.); andq is an integer from 0 to 8, in some embodiments, from 0 to 2, and inone embodiment, 0. In one particular embodiment, “q” is 0 and thepolymer is poly(3,4-ethylenedioxythiophene). One commercially suitableexample of a monomer suitable for forming such a polymer is3,4-ethylenedioxthiophene, which is available from Heraeus under thedesignation Clevios™ M.

The polymers of formula (I) are generally considered to be“extrinsically” conductive to the extent that they typically require thepresence of a separate counterion that is not covalently bound to thepolymer. The counterion may be a monomeric or polymeric anion thatcounteracts the charge of the conductive polymer. Polymeric anions can,for example, be anions of polymeric carboxylic acids (e.g., polyacrylicacids, polymethacrylic acid, polymaleic acids, etc.); polymeric sulfonicacids (e.g., polystyrene sulfonic acids (“PSS”), polyvinyl sulfonicacids, etc.); and so forth. The acids may also be copolymers, such ascopolymers of vinyl carboxylic and vinyl sulfonic acids with otherpolymerizable monomers, such as acrylic acid esters and styrene.Likewise, suitable monomeric anions include, for example, anions of C₁to C₂₀ alkane sulfonic acids (e.g., dodecane sulfonic acid); aliphaticperfluorosulfonic acids (e.g., trifluoromethane sulfonic acid,perfluorobutane sulfonic acid or perfluorooctane sulfonic acid);aliphatic C₁ to C₂₀ carboxylic acids (e.g., 2-ethyl-hexylcarboxylicacid); aliphatic perfluorocarboxylic acids (e.g., trifluoroacetic acidor perfluorooctanoic acid); aromatic sulfonic acids optionallysubstituted by C₁ to C₂₀ alkyl groups (e.g., benzene sulfonic acid,o-toluene sulfonic acid, p-toluene sulfonic acid or dodecylbenzenesulfonic acid); cycloalkane sulfonic acids (e.g., camphor sulfonic acidor tetrafluoroborates, hexafluorophosphates, perchlorates,hexafluoroantimonates, hexafluoroarsenates or hexachloroantimonates);and so forth. Particularly suitable counteranions are polymeric anions,such as a polymeric carboxylic or sulfonic acid (e.g., polystyrenesulfonic acid (“PSS”)). The molecular weight of such polymeric anionstypically ranges from about 1,000 to about 2,000,000, and in someembodiments, from about 2,000 to about 500,000.

Intrinsically conductive polymers may also be employed that have apositive charge located on the main chain that is at least partiallycompensated by anions covalently bound to the polymer. For example, oneexample of a suitable intrinsically conductive thiophene polymer mayhave repeating units of the following formula (II):

wherein,

R is (CH₂)_(a)—O—(CH₂)_(b)-L, where L is a bond or HC([CH₂]_(c)H);

a is from 0 to 10, in some embodiments from 0 to 6, and in someembodiments, from 1 to 4 (e.g., 1);

b is from 1 to 18, in some embodiments from 1 to 10, and in someembodiments, from 2 to 6 (e.g., 2, 3, 4, or 5);

c is from 0 to 10, in some embodiments from 0 to 6, and in someembodiments, from 1 to 4 (e.g., 1);

Z is an anion, such as SO₃ ⁻, C(O)O⁻, BF₄ ⁻, CF₃SO₃ ⁻, SbF₆ ⁻,N(SO₂CF₃)₂ ⁻, C₄H₃O₄ ⁻, ClO₄ ⁻, etc.; and

X is a cation, such as hydrogen, an alkali metal (e.g., lithium, sodium,rubidium, cesium or potassium), ammonium, etc.

In one particular embodiment, Z in formula (II) is a sulfonate ion suchthat the intrinsically conductive polymer contains repeating units ofthe following formula (III):

wherein, R and X are defined above. In formula (II) or (III), a ispreferably 1 and b is preferably 3 or 4. Likewise, X is preferablysodium or potassium.

If desired, the polymer may be a copolymer that contains other types ofrepeating units. In such embodiments, the repeating units of formula(II) typically constitute about 50 mol. % or more, in some embodimentsfrom about 75 mol. % to about 99 mol. %, and in some embodiments, fromabout 85 mol. % to about 95 mol. % of the total amount of repeatingunits in the copolymer. Of course, the polymer may also be a homopolymerto the extent that it contains 100 mol. % of the repeating units offormula (II). Specific examples of such homopolymers includepoly(4-(2,3-dihydrothieno-[3,4-b][1,4]dioxin-2-ylmethoxy)-1-butane-sulphonicacid, salt) andpoly(4-(2,3-dihydrothieno-[3,4-b][I,4]dioxin-2-ylmethoxy)-I-propanesulphonicacid, salt).

Regardless of the particular nature of the polymer, the resultingconductive polymer particles typically have an average size (e.g.,diameter) of from about 1 to about 80 nanometers, in some embodimentsfrom about 2 to about 70 nanometers, and in some embodiments, from about3 to about 60 nanometers. The diameter of the particles may bedetermined using known techniques, such as by ultracentrifuge, laserdiffraction, etc. The shape of the particles may likewise vary. In oneparticular embodiment, for instance, the particles are spherical inshape. However, it should be understood that other shapes are alsocontemplated by the present invention, such as plates, rods, discs,bars, tubes, irregular shapes, etc.

Although not necessarily required, the conductive polymer particles maybe applied in the form of a dispersion. The concentration of theconductive polymer in the dispersion may vary depending on the desiredviscosity of the dispersion and the particular manner in which thedispersion is to be applied to the capacitor element. Typically,however, the polymer constitutes from about 0.1 to about 10 wt. %, insome embodiments from about 0.4 to about 5 wt. %, and in someembodiments, from about 0.5 to about 4 wt. % of the dispersion. Thedispersion may also contain one or more components to enhance theoverall properties of the resulting solid electrolyte. For example, thedispersion may contain a binder to further enhance the adhesive natureof the polymeric layer and also increase the stability of the particleswithin the dispersion. The binder may be organic in nature, such aspolyvinyl alcohols, polyvinyl pyrrolidones, polyvinyl chlorides,polyvinyl acetates, polyvinyl butyrates, polyacrylic acid esters,polyacrylic acid amides, polymethacrylic acid esters, polymethacrylicacid amides, polyacrylonitriles, styrene/acrylic acid ester, vinylacetate/acrylic acid ester and ethylene/vinyl acetate copolymers,polybutadienes, polyisoprenes, polystyrenes, polyethers, polyesters,polycarbonates, polyurethanes, polyamides, polyimides, polysulfones,melamine formaldehyde resins, epoxide resins, silicone resins orcelluloses. Crosslinking agents may also be employed to enhance theadhesion capacity of the binders. Such crosslinking agents may include,for instance, melamine compounds, masked isocyanates or crosslinkablepolymers, such as polyurethanes, polyacrylates or polyolefins, andsubsequent crosslinking. Dispersion agents may also be employed tofacilitate the ability to apply the layer to the anode. Suitabledispersion agents include solvents, such as aliphatic alcohols (e.g.,methanol, ethanol, i-propanol and butanol), aliphatic ketones (e.g.,acetone and methyl ethyl ketones), aliphatic carboxylic acid esters(e.g., ethyl acetate and butyl acetate), aromatic hydrocarbons (e.g.,toluene and xylene), aliphatic hydrocarbons (e.g., hexane, heptane andcyclohexane), chlorinated hydrocarbons (e.g., dichloromethane anddichloroethane), aliphatic nitriles (e.g., acetonitrile), aliphaticsulfoxides and sulfones (e.g., dimethyl sulfoxide and sulfolane),aliphatic carboxylic acid amides (e.g., methylacetamide,dimethylacetamide and dimethylformamide), aliphatic and araliphaticethers (e.g., diethylether and anisole), water, and mixtures of any ofthe foregoing solvents. A particularly suitable dispersion agent iswater.

In addition to those mentioned above, still other ingredients may alsobe used in the dispersion. For example, conventional fillers may be usedthat have a size of from about 10 nanometers to about 100 micrometers,in some embodiments from about 50 nanometers to about 50 micrometers,and in some embodiments, from about 100 nanometers to about 30micrometers. Examples of such fillers include calcium carbonate,silicates, silica, calcium or barium sulfate, aluminum hydroxide, glassfibers or bulbs, wood flour, cellulose powder carbon black, electricallyconductive polymers, etc. The fillers may be introduced into thedispersion in powder form, but may also be present in another form, suchas fibers.

Surface-active substances may also be employed in the dispersion, suchas ionic or non-ionic surfactants. Furthermore, adhesives may beemployed, such as organofunctional silanes or their hydrolysates, forexample 3-glycidoxypropyltrialkoxysilane, 3-aminopropyl-triethoxysilane,3-mercaptopropyl-trimethoxysilane, 3-metacryloxypropyltrimethoxysilane,vinyltrimethoxysilane or octyltriethoxysilane. The dispersion may alsocontain additives that increase conductivity, such as ethergroup-containing compounds (e.g., tetrahydrofuran), lactonegroup-containing compounds (e.g., γ-butyrolactone or γ-valerolactone),amide or lactam group-containing compounds (e.g., caprolactam,N-methylcaprolactam, N,N-dimethylacetamide, N-methylacetamide,N,N-dimethylformamide (DMF), N-methylformamide, N-methylformanilide,N-methylpyrrolidone (NMP), N-octylpyrrolidone, or pyrrolidone), sulfonesand sulfoxides (e.g., sulfolane (tetramethylenesulfone) ordimethylsulfoxide (DMSO)), sugar or sugar derivatives (e.g., saccharose,glucose, fructose, or lactose), sugar alcohols (e.g., sorbitol ormannitol), furan derivatives (e.g., 2-furancarboxylic acid or3-furancarboxylic acid), an alcohols (e.g., ethylene glycol, glycerol,di- or triethylene glycol).

The dispersion may be applied using a variety of known techniques, suchas by spin coating, impregnation, pouring, dropwise application,injection, spraying, doctor blading, brushing, printing (e.g., ink-jet,screen, or pad printing), or dipping. The viscosity of the dispersion istypically from about 0.1 to about 100,000 mPas (measured at a shear rateof 100 s⁻¹), in some embodiments from about 1 to about 10,000 mPas, insome embodiments from about 10 to about 1,500 mPas, and in someembodiments, from about 100 to about 1000 mPas.

i. Inner Layers

The solid electrolyte is generally formed from one or more “inner”conductive polymer layers. The term “inner” in this context refers toone or more layers that overly the dielectric, whether directly or viaanother layer (e.g., pre-coat layer). One or multiple inner layers maybe employed. For example, the solid electrolyte typically contains from2 to 30, in some embodiments from 4 to 20, and in some embodiments, fromabout 5 to 15 inner layers (e.g., 10 layers). The inner layer(s) may,for example, contain intrinsically and/or extrinsically conductivepolymer particles such as described above. For instance, such particlesmay constitute about 50 wt. % or more, in some embodiments about 70 wt.% or more, and in some embodiments, about 90 wt. % or more (e.g., 100wt. %) of the inner layer(s). In alternative embodiments, the innerlayer(s) may contain an in-situ polymerized conductive polymer. In suchembodiments, the in-situ polymerized polymers may constitute about 50wt. % or more, in some embodiments about 70 wt. % or more, and in someembodiments, about 90 wt. % or more (e.g., 100 wt. %) of the innerlayer(s).

ii. Outer Layers

The solid electrolyte may also contain one or more optional “outer”conductive polymer layers that overly the inner layer(s) and are formedfrom a different material. For example, the outer layer(s) may containextrinsically conductive polymer particles. In one particularembodiment, the outer layer(s) are formed primarily from suchextrinsically conductive polymer particles in that they constitute about50 wt. % or more, in some embodiments about 70 wt. % or more, and insome embodiments, about 90 wt. % or more (e.g., 100 wt. %) of arespective outer layer. One or multiple outer layers may be employed.For example, the solid electrolyte may contain from 2 to 30, in someembodiments from 4 to 20, and in some embodiments, from about 5 to 15outer layers, each of which may optionally be formed from a dispersionof the extrinsically conductive polymer particles.

D. External Polymer Coating

An external polymer coating may also overly the solid electrolyte. Theexternal polymer coating may contain one or more layers formed frompre-polymerized conductive polymer particles such as described above(e.g., dispersion of extrinsically conductive polymer particles). Theexternal coating may be able to further penetrate into the edge regionof the capacitor body to increase the adhesion to the dielectric andresult in a more mechanically robust part, which may reduce equivalentseries resistance and leakage current. Because it is generally intendedto improve the degree of edge coverage rather to impregnate the interiorof the anode body, the particles used in the external coating typicallyhave a larger size than those employed in the solid electrolyte. Forexample, the ratio of the average size of the particles employed in theexternal polymer coating to the average size of the particles employedin any dispersion of the solid electrolyte is typically from about 1.5to about 30, in some embodiments from about 2 to about 20, and in someembodiments, from about 5 to about 15. For example, the particlesemployed in the dispersion of the external coating may have an averagesize of from about 80 to about 500 nanometers, in some embodiments fromabout 90 to about 250 nanometers, and in some embodiments, from about100 to about 200 nanometers.

If desired, a crosslinking agent may also be employed in the externalpolymer coating to enhance the degree of adhesion to the solidelectrolyte. Typically, the crosslinking agent is applied prior toapplication of the dispersion used in the external coating. Suitablecrosslinking agents are described, for instance, in U.S. PatentPublication No. 2007/0064376 to Merker, et al. and include, forinstance, amines (e.g., diamines, triamines, oligomer amines,polyamines, etc.); polyvalent metal cations, such as salts or compoundsof Mg, Al, Ca, Fe, Cr, Mn, Ba, Ti, Co, Ni, Cu, Ru, Ce or Zn, phosphoniumcompounds, sulfonium compounds, etc. Particularly suitable examplesinclude, for instance, 1,4-diaminocyclohexane,1,4-bis(amino-methyl)cyclohexane, ethylenediamine, 1,6-hexanediamine,1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine,1,10-decanediamine, 1,12-dodecanediamine, N,N-dimethylethylenediamine,N, N, N′,N′-tetramethylethylenediam ine, N, N,N′,N′-tetramethyl-1,4-butanediam ine, etc., as well as mixtures thereof.

The crosslinking agent is typically applied from a solution ordispersion whose pH is from 1 to 10, in some embodiments from 2 to 7, insome embodiments, from 3 to 6, as determined at 25° C. Acidic compoundsmay be employed to help achieve the desired pH level. Examples ofsolvents or dispersants for the crosslinking agent include water ororganic solvents, such as alcohols, ketones, carboxylic esters, etc. Thecrosslinking agent may be applied to the capacitor body by any knownprocess, such as spin-coating, impregnation, casting, dropwiseapplication, spray application, vapor deposition, sputtering,sublimation, knife-coating, painting or printing, for example inkjet,screen or pad printing. Once applied, the crosslinking agent may bedried prior to application of the polymer dispersion. This process maythen be repeated until the desired thickness is achieved. For example,the total thickness of the entire external polymer coating, includingthe crosslinking agent and dispersion layers, may range from about 1 toabout 50 μm, in some embodiments from about 2 to about 40 μm, and insome embodiments, from about 5 to about 20 μm.

E. Cathode Coating

If desired, the capacitor element may also employ a cathode coating thatoverlies the solid electrolyte and other optional layers (e.g., externalpolymer coating). The cathode coating may contain a metal particle layerincludes a plurality of conductive metal particles dispersed within apolymer matrix. The particles typically constitute from about 50 wt. %to about 99 wt. %, in some embodiments from about 60 wt. % to about 98wt. %, and in some embodiments, from about 70 wt. % to about 95 wt. % ofthe layer, while the polymer matrix typically constitutes from about 1wt. % to about 50 wt. %, in some embodiments from about 2 wt. % to about40 wt. %, and in some embodiments, from about 5 wt. % to about 30 wt. %of the layer.

The conductive metal particles may be formed from a variety of differentmetals, such as copper, nickel, silver, nickel, zinc, tin, lead, copper,aluminum, molybdenum, titanium, iron, zirconium, magnesium, etc., aswell as alloys thereof. Silver is a particularly suitable conductivemetal for use in the layer. The metal particles often have a relativelysmall size, such as an average size of from about 0.01 to about 50micrometers, in some embodiments from about 0.1 to about 40 micrometers,and in some embodiments, from about 1 to about 30 micrometers.Typically, only one metal particle layer is employed, although it shouldbe understood that multiple layers may be employed if so desired. Thetotal thickness of such layer(s) is typically within the range of fromabout 1 μm to about 500 μm, in some embodiments from about 5 μm to about200 μm, and in some embodiments, from about 10 μm to about 100 μm.

The polymer matrix typically includes a polymer, which may bethermoplastic or thermosetting in nature. Typically, however, thepolymer is selected so that it can act as a barrier to electromigrationof silver ions, and also so that it contains a relatively small amountof polar groups to minimize the degree of water adsorption in thecathode coating. In this regard, the present inventors have found thatvinyl acetal polymers are particularly suitable for this purpose, suchas polyvinyl butyral, polyvinyl formal, etc. Polyvinyl butyral, forinstance, may be formed by reacting polyvinyl alcohol with an aldehyde(e.g., butyraldehyde). Because this reaction is not typically complete,polyvinyl butyral will generally have a residual hydroxyl content. Byminimizing this content, however, the polymer can possess a lesserdegree of strong polar groups, which would otherwise result in a highdegree of moisture adsorption and result in silver ion migration. Forinstance, the residual hydroxyl content in polyvinyl acetal may be about35 mol. % or less, in some embodiments about 30 mol. % or less, and insome embodiments, from about 10 mol. % to about 25 mol. %. Onecommercially available example of such a polymer is available fromSekisui Chemical Co., Ltd. under the designation “BH-S” (polyvinylbutyral).

To form the cathode coating, a conductive paste is typically applied tothe capacitor that overlies the solid electrolyte. One or more organicsolvents are generally employed in the paste. A variety of differentorganic solvents may generally be employed, such as glycols (e.g.,propylene glycol, butylene glycol, triethylene glycol, hexylene glycol,polyethylene glycols, ethoxydiglycol, and dipropyleneglycol); glycolethers (e.g., methyl glycol ether, ethyl glycol ether, and isopropylglycol ether); ethers (e.g., diethyl ether and tetrahydrofuran);alcohols (e.g., benzyl alcohol, methanol, ethanol, n-propanol,iso-propanol, and butanol); triglycerides; ketones (e.g., acetone,methyl ethyl ketone, and methyl isobutyl ketone); esters (e.g., ethylacetate, butyl acetate, diethylene glycol ether acetate, andmethoxypropyl acetate); amides (e.g., dimethylformamide,dimethylacetamide, dimethylcaprylic/capric fatty acid amide andN-alkylpyrrolidones); nitriles (e.g., acetonitrile, propionitrile,butyronitrile and benzonitrile); sulfoxides or sulfones (e.g., dimethylsulfoxide (DMSO) and sulfolane); etc., as well as mixtures thereof. Theorganic solvent(s) typically constitute from about 10 wt. % to about 70wt. %, in some embodiments from about 20 wt. % to about 65 wt. %, and insome embodiments, from about 30 wt. % to about 60 wt. % of the paste.Typically, the metal particles constitute from about 10 wt. % to about60 wt. %, in some embodiments from about 20 wt. % to about 45 wt. %, andin some embodiments, from about 25 wt. % to about 40 wt. % of the paste,and the resinous matrix constitutes from about 0.1 wt. % to about 20 wt.%, in some embodiments from about 0.2 wt. % to about 10 wt. %, and insome embodiments, from about 0.5 wt. % to about 8 wt. % of the paste.

The paste may have a relatively low viscosity, allowing it to be readilyhandled and applied to a capacitor element. The viscosity may, forinstance, range from about 50 to about 3,000 centipoise, in someembodiments from about 100 to about 2,000 centipoise, and in someembodiments, from about 200 to about 1,000 centipoise, such as measuredwith a Brookfield DV-1 viscometer (cone and plate) operating at a speedof 10 rpm and a temperature of 25° C. If desired, thickeners or otherviscosity modifiers may be employed in the paste to increase or decreaseviscosity. Further, the thickness of the applied paste may also berelatively thin and still achieve the desired properties. For example,the thickness of the paste may be from about 0.01 to about 50micrometers, in some embodiments from about 0.5 to about 30 micrometers,and in some embodiments, from about 1 to about 25 micrometers. Onceapplied, the metal paste may be optionally dried to remove certaincomponents, such as the organic solvents. For instance, drying may occurat a temperature of from about 20° C. to about 150° C., in someembodiments from about 50° C. to about 140° C., and in some embodiments,from about 80° C. to about 130° C.

F. Other Components

If desired, the capacitor may also contain other layers as is known inthe art. In certain embodiments, for instance, a carbon layer (e.g.,graphite) may be positioned between the solid electrolyte and the silverlayer that can help further limit contact of the silver layer with thesolid electrolyte. In addition, a pre-coat layer may also be employedthat overlies the dielectric and includes an organometallic compound,such as described in more detail below.

II. Terminations

Once the desired layers are formed, the capacitor may be provided withterminations as indicated above. More particularly, the capacitorcontains an anode termination to which an anode lead of the capacitorelement is electrically connected and a cathode termination to which thesolid electrolyte of the capacitor element is electrically connected.Any conductive material may be employed to form the terminations, suchas a conductive metal (e.g., copper, nickel, silver, nickel, zinc, tin,palladium, lead, copper, aluminum, molybdenum, titanium, iron,zirconium, magnesium, and alloys thereof). Particularly suitableconductive metals include, for instance, copper, copper alloys (e.g.,copper-zirconium, copper-magnesium, copper-zinc, or copper-iron),nickel, and nickel alloys (e.g., nickel-iron). The thickness of theterminations is generally selected to minimize the thickness of thecapacitor. For instance, the thickness of the terminations may rangefrom about 0.05 to about 1 millimeter, in some embodiments from about0.05 to about 0.5 millimeters, and from about 0.07 to about 0.2millimeters. One exemplary conductive material is a copper-iron alloymetal plate available from Wieland (Germany). If desired, the surface ofthe terminations may be electroplated with nickel, silver, gold, tin,etc. as is known in the art to ensure that the final part is mountableto the circuit board. In one particular embodiment, both surfaces of theterminations are plated with nickel and silver flashes, respectively,while the mounting surface is also plated with a tin solder layer.

The terminations may be connected to the capacitor element using anytechnique known in the art. In one embodiment, for example, a lead framemay be provided that defines the cathode termination and anodetermination. To attach the capacitor element to the lead frame, aconductive adhesive may initially be applied to a surface of the cathodetermination. The conductive adhesive may include, for instance,conductive metal particles contained with a resin composition. The metalparticles may be silver, copper, gold, platinum, nickel, zinc, bismuth,etc. The resin composition may include a thermoset resin (e.g., epoxyresin), curing agent (e.g., acid anhydride), and coupling agent (e.g.,silane coupling agents). Suitable conductive adhesives may be describedin U.S. Patent Application Publication No. 2006/0038304 to Osako, et al.Any of a variety of techniques may be used to apply the conductiveadhesive to the cathode termination. Printing techniques, for instance,may be employed due to their practical and cost-saving benefits. Theanode lead may also be electrically connected to the anode terminationusing any technique known in the art, such as mechanical welding, laserwelding, conductive adhesives, etc. Upon electrically connecting theanode lead to the anode termination, the conductive adhesive may then becured to ensure that the electrolytic capacitor is adequately adhered tothe cathode termination.

Referring to FIG. 1, for example, a capacitor 30 is shown as includingan anode termination 62 and a cathode termination 72 in electricalconnection with a capacitor element 33 having an upper surface 37, lowersurface 39, front surface 36, rear surface 38, first side surface 35,and opposing side surface (not shown). The cathode termination 72 may beprovided in electrical contact with any surface of the capacitorelement, such as via a conductive adhesive. In the illustratedembodiment, for example, the cathode termination 72 contains a firstcomponent 73 that is generally parallel and adjacent to the uppersurface 37 and a second component 75 that is generally parallel andadjacent to the lower surface 39. The first component 73 is also inelectrical contact with the upper surface 37. The cathode termination 72may also contain a third component 77 generally extends in a directionperpendicular to the first component 73 and second component 75. Ifdesired, the third component 77 may also be provided in electricalcontact with the rear surface 38 of the capacitor element 33. The anodetermination 62 likewise contains a first component 63 that is generallyparallel to the lower surface 39 of the capacitor element 33 and asecond component 67 that is generally parallel to the anode lead 16.Further, the anode termination 62 may include a third component 64 thatis generally perpendicular to the first component 63 and a fourthcomponent 69 that is generally perpendicular to the second component 67and located adjacent to the anode lead 16. In the illustratedembodiment, the second component 67 and fourth component 69 define aregion 51 for connection to the anode lead 16. Although not depicted inFIG. 1, the region 51 may possess a “U-shape” to further enhance surfacecontact and mechanical stability of the lead 16.

The terminations may be connected to the capacitor element using anytechnique known in the art. In one embodiment, for example, a lead framemay be provided that defines the cathode termination 72 and anodetermination 62. To attach the capacitor element 33 to the lead frame, aconductive adhesive 49 may initially be applied to a surface of thecathode termination 72. In one embodiment, the anode termination 62 andcathode termination 72 are folded into the position shown in FIG. 1.Thereafter, the capacitor element 33 is positioned on the cathodetermination 72 so that its lower surface 39 contacts the adhesive 49 andthe anode lead 16 contacts the region 51. The anode lead 16 is thenelectrically connected to the region 51 using any technique known in theart, such as mechanical welding, laser welding, conductive adhesives,etc. For example, the anode lead 16 may be welded to the anodetermination 62 using a laser. Lasers generally contain resonators thatinclude a laser medium capable of releasing photons by stimulatedemission and an energy source that excites the elements of the lasermedium. One type of suitable laser is one in which the laser mediumconsist of an aluminum and yttrium garnet (YAG), doped with neodymium(Nd). The excited particles are neodymium ions Nd³⁺. The energy sourcemay provide continuous energy to the laser medium to emit a continuouslaser beam or energy discharges to emit a pulsed laser beam. Uponelectrically connecting the anode lead 16 to the anode termination 62,the conductive adhesive may then be cured. For example, a heat press maybe used to apply heat and pressure to ensure that the electrolyticcapacitor element 33 is adequately adhered to the cathode termination 72by the adhesive 49.

To help further minimize the likelihood of delamination, an interfacialcoating may also be employed that covers at least a portion of the anodetermination and/or cathode termination and is in contact with the casingmaterial. In contrast to the metal components commonly employed in theanode and cathode terminations, the interfacial coating may be formedfrom a resinous material that has a coefficient of thermal expansionsimilar in nature to the curable resinous matrix used in the casingmaterial. Again, this can further reduce the likelihood that anyexpansion of the casing material during manufacturing will result indelamination from the anode lead and/or capacitor element.

One or multiple coatings may be employed. In one embodiment, forinstance, an interfacial coating may be employed that covers at least aportion of the anode termination. In such embodiments, the coating mayalso contact at least a portion of a surface of the capacitor element,such as a front surface, bottom surface, and/or top surface of thecapacitor element. Likewise, the coating may also contact at least aportion of the anode lead. In another embodiment, an interfacial coatingmay be employed that covers at least a portion of the cathodetermination. In such embodiments, the coating may also contact at leasta portion of a surface of the capacitor element, such as a rear surface,top surface, and/or bottom surface. Referring again to FIG. 1, forexample, the capacitor 30 is shown with an interfacial coating 90 thatis on the anode termination 62. More particularly, in the illustratedembodiment, the coating 90 is in contact with the second component 67and the fourth component 69 of the anode termination 62 so that theregion 51 is generally covered. The coating 90 is also in contact withat least a portion of the anode lead 16, particularly at those locationssurrounding the region 51 at which the lead 16 is connected to the anodetermination 62. Of course, it should be understood that the coating mayalso be provided in other configurations and disposed on any surfacedesired. In one embodiment, for example, the coating may contact onlythe second component 67 of the anode termination 62.

Regardless of where it is located, the resinous material employed in theinterfacial coating may be selectively controlled to impart certaindesired properties to the resulting capacitor. In one embodiment, forinstance, the interfacial coating may include a hydrophobic resinousmaterial, such as a low surface energy polymer (e.g., fluoropolymer,silicone), organometallic compound, etc. Fluoropolymers, for instance,may contain a hydrocarbon backbone polymer (e.g., polyolefin) in whichsome or all of the hydrogen atoms are substituted with fluorine groups,such as fluoroalkyl groups (e.g., trifluoromethyl, trifluoroethyl,etc.). The backbone polymer may likewise be formed from ethylenicallyunsaturated monomers (e.g., olefins, olefinic acyrlates, olefinicmethacrylates, etc.). Suitable monomers may, for instance, have a carbonchain length of from 3 to 20 atoms, in some embodiments from 6 to 12carbon atoms in length, and in some embodiments, from 8 to 10 carbonatoms in length. Particularly suitable fluoroalkyl-substituted monomersfor use in the present invention are fluoroalkyl (meth)acrylates, suchas perfluorohexyl (meth)acrylate, perfluoroheptyl (meth)acrylate,perfluorooctyl (meth)acrylate, perfluorononyl perfluorodecyl(meth)acrylate, perfluoroundecyl (meth)acrylate or perfluorododecyl(meth)acrylate, etc., as well as mixtures thereof. As used herein, theterm “(meth)acrylic” includes both acrylate and methacrylate monomers.

Another suitable low surface energy polymer that may be employed is asilicone polymer. Such polymers are typically derived frompolyorganosiloxanes, such as those having the following general formula(IV):

wherein,

y is an integer greater than 1; and

R₈, R₉, R₁₀, R₁₁, R₁₂, R₁₃, R₁₄, and R₁₅ are independently monovalentgroups typically containing from 1 to about 20 carbon atoms, such asalkyl groups (e.g., methyl, ethyl, propyl, pentyl, octyl, undecyl,octadecyl, etc.); alkoxy groups (e.g., methoxy, ethoxy, propoxy, etc.);carboxyalkyl groups (e.g., acetyl); cycloalkyl groups (e.g.,cyclohexyl); alkenyl groups (e.g., vinyl, allyl, butenyl, hexenyl,etc.); aryl groups (e.g., phenyl, tolyl, xylyl, benzyl, 2-phenylethyl,etc.); and halogenated hydrocarbon groups (e.g., 3,3,3-trifluoropropyl,3-chloropropyl, dichlorophenyl, etc.). Examples of suchpolyorganosiloxanes may include, for instance, polydimethylsiloxane(“PDMS”), polymethylhydrogensiloxane, dimethyidiphenylpolysiloxane,dimethyl/methylphenylpolysiloxane, polymethylphenylsiloxane,methylphenyl/dimethylsiloxane, vinyldimethyl terminatedpolydimethylsiloxane, vinylmethyl/dimethylpolysiloxane, vinyldimethylterminated vinylmethyl/dimethylpolysiloxane, divinylmethyl terminatedpolydimethylsiloxane, vinylphenylmethyl terminated polydimethylsiloxane,dimethylhydro terminated polydimethylsiloxane,methylhydro/dimethylpolysiloxane, methylhydro terminatedmethyloctylpolysiloxane, methylhydro/phenylmethyl polysiloxane,fluoro-modified polysiloxane, etc. To form the hydrophobic material, thepolyorganosiloxane may be crosslinked using any of a variety of knowntechniques, such as by catalyst curing (e.g., platinum catalysts), roomtemperature vulcanization, moisture curing, etc. Crosslinking agents maybe employed, such as alkoxy silanes having the formula Si—OR, wherein Ris H, alkyl (e.g., methyl), alkenyl, carboxyalkyl (e.g., acetyl), and soforth.

Of course, still other hydrophobic materials may also be employed in theinterfacial coating. In one embodiment, for instance, the hydrophobicmaterial may include an organometallic compound, such as those havingthe following general formula (V):

wherein,

M is an organometallic atom, such as silicon, titanium, and so forth;

R₁₆, R₁₇, and R₁₈ are independently an alkyl (e.g., methyl, ethyl,propyl, etc.) or a hydroxyalkyl (e.g., hydroxymethyl, hydroxyethyl,hydroxypropyl, etc.), wherein at least one of R₁₆, R₁₇, and R₁₈ is ahydroxyalkyl;

n is an integer from 0 to 8, in some embodiments from 1 to 6, and insome embodiments, from 2 to 4 (e.g., 3); and

X is an organic or inorganic functional group, such as glycidyl,glycidyloxy, mercapto, amino, vinyl, etc.

In certain embodiments, R₁₆, R₁₇, and R₁₈ may a hydroxyalkyl (e.g.,OCH₃). In other embodiments, however, R₁₆ may be an alkyl (e.g., CH₃)and R₁₇ and R₁₈ may a hydroxyalkyl (e.g., OCH₃).

In certain embodiments, M may be silicon so that the organometalliccompound is an organosilane compound, such as an alkoxysilane. Suitablealkoxysilanes may include, for instance, 3-aminopropyltrimethoxysilane,3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane,3-aminopropylmethyldiethoxysilane,3-(2-aminoethyl)aminopropyltrimethoxysilane,3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane,3-mercaptopropylmethyldimethoxysilane,3-mercaptopropylmethyldiethoxysilane, glycidoxymethyltrimethoxysilane,glycidoxymethyltriethoxysilane, glycidoxymethyl-tripropoxysilane,glycidoxymethyltributoxysilane, β-glycidoxyethyltrimethoxysilane,β-glycidoxyethyltriethoxysilane, β-glycidoxyethyl-tripropoxysilane,β-glycidoxyethyl-tributoxysilane, β-glycidoxyethyltrimethoxysilane,α-glycidoxyethyltriethoxysilane, α-glycidoxyethyltripropoxysilane,α-glycidoxyethyltributoxysilane, γ-glycidoxypropyl-trimethoxysilane,γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyl-tripropoxysilane,γ-glycidoxypropyltributoxysilane, β-glycidoxypropyltrimethoxysilane,β-glycidoxypropyl-triethoxysilane, 3-glycidoxypropyltripropoxysilane,α-glycidoxypropyltributoxysilane, α-glycidoxypropyltrimethoxysilane,α-glycidoxypropyltriethoxysilane, α-glycidoxypropyl-tripropoxysilane,α-glycidoxypropyltributoxysilane, γ-glycidoxybutyltrimethoxysilane,δ-glycidoxybutyltriethoxysilane, δ-glycidoxybutyltripropoxysilane,δ-glycidoxybutyl-tributoxysilane, δ-glycidoxybutyltrimethoxysilane,γ-glycidoxybutyltriethoxysilane, γ-glycidoxybutyltripropoxysilane,γ-propoxybutyltributoxysilane, δ-glycidoxybutyl-trimethoxysilane,δ-glycidoxybutyltriethoxysilane, δ-glycidoxybutyltripropoxysilane,α-glycidoxybutyltrim ethoxysilane, α-glycidoxybutyltriethoxysilane,α-glycidoxybutyltripropoxysilane, α-glycidoxybutyltributoxysilane,(3,4-epoxycyclohexyl)-methyltrimethoxysilane,(3,4-epoxycyclohexyl)methyl-triethoxysilane,(3,4-epoxycyclohexyl)methyltripropoxysilane,(3,4-epoxycyclohexyl)-methyltributoxysilane,(3,4-epoxycyclohexyl)ethyl-trimethoxysilane,(3,4-epoxycyclohexyl)ethyl-triethoxysilane,(3,4-epoxycyclohexyl)ethyltripropoxysilane,(3,4-epoxycyclohexyl)ethyltributoxysilane,(3,4-epoxycyclohexyl)propyltrimethoxysilane,(3,4-epoxycyclohexyl)propyltriethoxysilane,(3,4-epoxycyclohexyl)propyltripropoxysilane,(3,4-epoxycyclohexyl)propyltributoxysilane,(3,4-epoxycyclohexyl)butyltrimethoxysilane, (3,4-epoxycyclohexy)butyltriethoxysilane, (3,4-epoxycyclohexyl)butyltripropoxysilane,(3,4-epoxycyclohexyl)butyltributoxysilane, and so forth.

To help aid in its application, the interfacial coating may be initiallyprovided in the form of a coating formulation that contains thehydrophobic resinous material in combination with an organic solvent,which is typically a liquid at room temperature. When employed, suchsolvents typically constitute from about 90 wt. % to about 99.9 wt. %,in some embodiments from about 92 wt. % to about 99.8 wt. %, and in someembodiments, from about 95 wt. % to about 99.5 wt. % of the formulation,while the hydrophobic resinous material may constitute from about 0.1wt. % to about 10 wt. %, in some embodiments from about 0.2 wt. % toabout 8 wt. %, and in some embodiments, from about 0.5 wt. % to about 5wt. % of the solution. The solvent(s) employed will depend in part onthe nature of the resinous material, but generally include organicalcohols, hydrocarbon solvents, fluorinated hydrocarbon solvents, etc.For example, particularly suitable solvents for use with fluoropolymersinclude fluorinated hydrocarbon solvents, such as hydrofluoroethers,fluorinated ketones, fluorinated olefins, etc. In one particularembodiment, for instance, the coating formulation may contain ahydrofluoroether having the following general formula (VI):(R¹—O)_(x)—R²  (VI)

wherein:

x is 1 or 2;

one of R¹ and R² is a perfluoroaliphatic or perfluorocyclic group andthe other is an aliphatic or a cyclic hydrocarbon group. For example, R¹and/or R² may include substituted and nonsubstituted alkyl, aryl, andalkylaryl groups and their derivatives. Representative examples ofsuitable hydrofluoroethers include the following compounds: C₅F₁₁OC₂H₅,C₃F₇OCH₃, C₄F₉OCH₃, C₄F₉OC₂H₅, C₃F₇OCF(CF₃)CF₂OCH₃, C₄F₉OC₂F₄OC₂F₄OC₂H₅,C₄F₉O(CF₂)₃OCH₃, C₃F₇CF(OC₂H₅)CF(CF₃)₂, C₂F₅CF(OCH₃)CF(CF₃)₂,C₄F₉OC₂H₄OC₄F₉, etc. Particularly suitable are ethyl nonafluoroisobutylether and ethyl nonafluorobutyl ether, both of which are represented bythe structure, C₄F₉₀C₂H₅.

III. Casing Material

As indicated, the capacitor element and anode lead are generallyencapsulated with a casing material so that at least a portion of theanode and cathode terminations are exposed for mounting onto a circuitboard. Referring again to FIG. 1, for instance, the capacitor element 33and anode lead 16 may be encapsulated within a casing material 28 sothat a portion of the anode termination 62 and a portion of the cathodetermination 72 remain exposed. As indicated above, the resinous matrixused to form the casing material has a relatively low coefficient ofthermal expansion, which helps reduce the likelihood that it willdelaminate from the capacitor element when exposed to the hightemperatures. The resinous matrix is also generally hydrophobic innature.

In certain embodiments, for example, the resinous matrix may contain apolycyanate containing at least two cyanate ester groups. When cured,for example, the polycyanate may form a polycyanurate having a triazinering. Due to the high degree of symmetry in the triazine ring, wheredipoles associated with the carbon-nitrogen and carbon-oxygen bonds arecounterbalanced, the resulting polycyanurate can exhibit a relativelylow degree of thermal expansion. Suitable polycyanates may include, forinstance, bisphenol A dicyanate; the dicyanates of4,4′-dihydroxydiphenyl, 4,4′-dihydroxydiphenyl oxide, resorcinyl,hydroquinone, 4,4′-thiodiphenol, 4,4′-sulfonyldiphenyl,3,3′,5,5′-tetrabromobisphenol A, 2,2′,6,6′-tetrabromobisphenol A,2,2′-dihydroxydiphenyl, 3,3′-dimethoxybisphenol A,4,4′-dihydroxydiphenylcarbonate, dicyclopentadiene diphenol,4,4′-dihydroxybenzophenone, 4,4′-dihydroxydiphenylmethane,tricyclopentadiene diphenol, etc.; the tricyanate oftris(hydroxyphenyl)methane, the tetracyanate of2,2′,4,4′-tetrahydroxydiphenyl methane, the polycyanate of aphenolformaldehyde condensation product (novolac); the polycyanate of adicyclopentadiene and phenol condensation product; and so forth. Ifdesired, the polycyanate may also contain one or more polycyclicaliphatic radicals containing two or more cyclic rings, such as a C₇-C₂₀polycyclic aliphatic radical, including cyclopentadiene, norbornane,bornane, norbornadiene, trahydroindene, methyltetrahydroindene,dicyclopentadiene, bicyclo-(2,2,I)-hepta-2,5-diene,5-methylene-2-norbornene, 5-ethylidene-2-norbornene,5-propenyl-2-norbornene, 5-(4-cyclopentenyl)-2-norbornene,5-cyclohexylidene-2-norbornene, 5-vinyl-2-norbornene, etc. In oneparticular embodiment, for instance, the polycyanate may be adicyclopentadiene bisphenol cyanate ester. Without intending to belimited by theory, it is believed such polycyclic radicals can act as anonpolar bridging group for the polycyanate, which helps improve theresistance to thermal expansion.

The resinous matrix may also contain an epoxy resin, either alone or incombination with a polycyanate. When used in combination, the epoxyresin can react with the polycyanate to form a copolymer and/orcrosslink with the polycyanate resin when cured. Examples of suitableepoxy resins include, for instance, bisphenol A type epoxy resins,bisphenol F type epoxy resins, phenol novolac type epoxy resins,orthocresol novolac type epoxy resins, brominated epoxy resins andbiphenyl type epoxy resins, cyclic aliphatic epoxy resins, glycidylester type epoxy resins, glycidylamine type epoxy resins, cresol novolactype epoxy resins, naphthalene type epoxy resins, phenol aralkyl typeepoxy resins, cyclopentadiene type epoxy resins, heterocyclic epoxyresins, etc. To help provide the desired degree of resistance to thermalexpansion, however, it is particularly desirable to employ epoxy phenolnovolac (“EPN”) resins, which are glycidyl ethers of phenolic novolacresins. These resins can be prepared, for example, by reaction ofphenols with an excess of formaldehyde in the presence of an acidiccatalyst to produce the phenolic novolac resin. Novolac epoxy resins arethen prepared by reacting the phenolic novolac resin withepichlorihydrin in the presence of sodium hydroxide. Specific examplesof the novolac-type epoxy resins include a phenol-novolac epoxy resin,cresol-novolac epoxy resin, naphthol-novolac epoxy resin,naphthol-phenol co-condensation novolac epoxy resin, naphthol-cresolco-condensation novolac epoxy resin, brominated phenol-novolac epoxyresin, etc. Regardless of the type of resin selected, the resultingphenolic novolac epoxy resins typically have more than two oxiranegroups and can be used to produce cured coating compositions with a highcrosslinking density, which can be particularly suitable for enhancingresistance to thermal expansion. One such phenolic novolac epoxy resinis poly[(phenyl glycidyl ether)-co-formaldehyde]. Other suitable resinsare commercially available under the trade designation ARALDITE (e.g.,GY289, EPN 1183, EP 1179, EPN 1139, and EPN 1138) from Huntsman.

The polycyanate and/or epoxy resin may be crosslinked with a co-reactant(hardener) to further improve the mechanical properties of thecomposition and also enhance its resistance to thermal expansion e asnoted above. Examples of such co-reactants may include, for instance,polyamides, amidoamines (e.g., aromatic amidoamines such asaminobenzamides, aminobenzanilides, and aminobenzenesulfonamides),aromatic diamines (e.g., diaminodiphenylmethane, diaminodiphenylsulfone,etc.), aminobenzoates (e.g., trimethylene glycol di-p-aminobenzoate andneopentyl glycol di-p-amino-benzoate), aliphatic amines (e.g.,triethylenetetramine, isophoronediamine), cycloaliphatic amines (e.g.,isophorone diamine), imidazole derivatives, guanidines (e.g.,tetramethylguanidine), carboxylic acid anhydrides (e.g.,methylhexahydrophthalic anhydride), carboxylic acid hydrazides (e.g.,adipic acid hydrazide), phenolic-novolac resins (e.g., phenol novolac,cresol novolac, etc.), carboxylic acid amides, etc., as well ascombinations thereof. Phenolic-novolac resins may be particularlysuitable for use in the present invention.

The casing material may also contain an inorganic oxide filler. Suchfillers are typically maintained at a high level of the casing material,such as from about 75 wt. % to about 99.5 wt. %, in some embodimentsfrom about 76 wt. % to about 99 wt. %, and in some embodiments, fromabout 77 wt. % to about 90 wt. % of the casing material, while theresinous matrix typically constitutes from about 0.5 wt. % to about 25wt. %, in some embodiments from about 1 wt. % to about 24 wt. %, and insome embodiments, from about 10 wt. % to about 23 wt. % of the casingmaterial. The nature of the inorganic oxide fillers may vary, such assilica, alumina, zirconia, magnesium oxides, iron oxides (e.g., ironhydroxide oxide yellow), titanium oxides (e.g., titanium dioxide), zincoxides (e.g., boron zinc hydroxide oxide), copper oxides, zeolites,silicates, clays (e.g., smectite clay), etc., as well as composites(e.g., alumina-coated silica particles) and mixtures thereof. Regardlessof the particular fillers employed, however, a substantial portion, ifnot all, of the inorganic oxide fillers is typically in the form ofvitreous silica, which is believed to further improve the moistureresistance of the casing material due to its high purity and relativelysimple chemical form. Vitreous silica may, for instance, constituteabout 30 wt. % or more, in some embodiments from about 35 wt. % to about90 wt. %, and in some embodiments, from about 40 wt. % to about 80 wt. %of the total weight of fillers employed in the composition, as well asfrom about 20 wt. % to about 70 wt. %, in some embodiments from about 25wt. % to about 65 wt. %, and in some embodiments, from about 30 wt. % toabout 60 wt. % of the entire composition. Of course, other forms ofsilica may also be employed in combination with the vitreous silica,such as quartz, fumed silica, cristabolite, etc.

Apart from the components noted above, it should be understood thatstill other additives may also be employed in the casing material, suchas photoinitiators, viscosity modifiers, suspension aiding agents,pigments, stress reducing agents, coupling agents (e.g., silane couplingagents), stabilizers, etc. When employed, such additives typicallyconstitute from about 0.1 to about 20 wt. % of the total composition.

The particular manner in which the casing material is applied to thecapacitor element may vary as desired. In one particular embodiment, thecapacitor element is placed in a mold and the casing material is appliedto the capacitor element so that it occupies the spaces defined by themold and leaves exposed at least a portion of the anode and cathodeterminations. The casing material may be initially provided in the formof a single or multiple compositions. For instance, a first compositionmay contain the resinous matrix and filler and the second compositionmay contain a co-reactant. Regardless, once it is applied, the casingmaterial may be heated or allowed to stand at ambient temperatures sothat the resinous matrix is allowed to crosslink with the co-reactant,which thereby causes the casing material to cure and harden into thedesired shape of the case. For instance, the casing material may beheated to a temperature of from about 15° C. to about 150° C., in someembodiments from about 20° C. to about 120° C., and in some embodiments,from about 25° C. to about 100° C.

Although by no means required, a moisture barrier layer may also beemployed that coats all or a portion of the casing material. Themoisture barrier layer is generally formed from a hydrophobic materialsuch as described above, e.g., silicone, fluoropolymer, organometalliccompound, etc.

The present invention may be better understood by reference to thefollowing examples.

Test Procedures

Capacitance

The capacitance may be measured using a Keithley 3330 Precision LCZmeter with Kelvin Leads with 2.2 volt DC bias and a 0.5 volt peak topeak sinusoidal signal. The operating frequency may be 120 Hz and thetemperature may be 23° C.±2° C. In some cases, the “wet-to-dry”capacitance can be determined. The “dry capacitance” refers to thecapacitance of the part before application of the solid electrolyte,graphite, and silver layers, while the “wet capacitance” refers to thecapacitance of the part after formation of the dielectric, measured in14% nitric acid in reference to 1 mF tantalum cathode with 10 volt DCbias and a 0.5 volt peak to peak sinusoidal signal after 30 seconds ofelectrolyte soaking.

Equivalent Series Resistance (ESR)

Equivalence series resistance may be measured using a Keithley 3330Precision LCZ meter with Kelvin Leads 2.2 volt DC bias and a 0.5 voltpeak to peak sinusoidal signal. The operating frequency may 100 kHz andthe temperature may be 23° C.±2° C.

Dissipation Factor

The dissipation factor may be measured using a Keithley 3330 PrecisionLCZ meter with Kelvin Leads with 2.2 volt DC bias and a 0.5 volt peak topeak sinusoidal signal. The operating frequency may be 120 Hz and thetemperature may be 23° C.±2° C.

Leakage Current

Leakage current may be measured using a leakage test meter at atemperature of 23° C.±2° C. and at the rated voltage after a minimum of60 seconds.

High Temperature Storage Testing

High temperature storage testing is based on IEC 60068-2-2:2007(condition Bb, temperature 125° C.). All measurements of ESR areconducted at temperature 23° C.±2° C. after 1 to 2 hours of recoveryfrom the test conditions. The samples are not mounted on a substrate.The ratio of the actual ESR (average) of all tested units to the initialESR (average) is determined for various samples (e.g., twenty five (25)samples).

Example 1

50,000 μFV/g tantalum powder was used to form anode samples. Each anodesample was embedded with a tantalum wire, sintered at 1350° C., andpressed to a density of 5.8 g/cm³. The resulting pellets had a size of1.7×2.4×1.0 mm. The pellets were anodized to 23.5 volts inwater/phosphoric acid electrolyte with a conductivity of 8.6 mS/cm at atemperature of 85° C. to form the dielectric layer. The pellets wereanodized again to 80 volts in a water/boric acid/disodium tetraboratewith a conductivity of 2.0 mS/cm at a temperature of 30° C. for 25seconds to form a thicker oxide layer built up on the outside.

A conductive polymer coating was then formed by dipping the anode into abutanol solution of iron (III) toluenesulfonate (Clevios™ C, H. C.Starck) and consequently into 3,4-ethylenedioxythiophene (Clevios™ M, H.C. Starck) and polymerized. After 45 minutes of polymerization, a thinlayer of poly(3,4-ethylenedioxythiophene) was formed on the surface ofthe dielectric. The anode was washed in methanol to remove reactionby-products, anodized in a liquid electrolyte, and washed again inmethanol. This process was repeated 6 times. Thereafter, the parts weredipped into a dispersed poly(3,4-ethylenedioxythiophene) having a solidscontent of 2.0% and viscosity 20 mPa·s (Clevios™ K, Heraeus). Uponcoating, the parts were dried at 125° C. for 20 minutes. This processwas repeated 3 times. Thereafter, the parts were dipped into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content of 2.0% andviscosity 160 mPa·s (Clevios™ K, Heraeus). Upon coating, the parts weredried at 125° C. for 20 minutes. This process was repeated 12 times. Theparts were then dipped into a graphite dispersion and dried. Finally,the parts were dipped into a silver dispersion and dried. Multiple parts(2,000) of 47 μF/10V capacitors were made in this manner andencapsulated in a silica-filled resin having a temperature coefficientof 13 ppm/° C. at a temperature below the glass transition temperatureand 51 ppm/° C. at a temperature above the glass transition temperature.

Example 2

Capacitors were formed in the manner described in Example 1, except thatthe resulting parts were encapsulated in a resinous matrix as describedherein. Twenty five (25) parts of 47 μF/10V capacitors were formed andthen subjected to high temperature storage testing as indicated above.The results are set forth below in Table 1.

TABLE 1 High Temperature Storage Testing Average Ratio of ActualESR/Initial ESR Test time (hours) EXAMPLE 1 EXAMPLE 2 0 1.00 1.00 961.03 1.00 240 1.14 1.00 420 1.37 1.00 560 2.13 1.01 750 4.56 1.02 1,00011.57 1.03 1,250 30.84 1.04

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

What is claimed is:
 1. A solid electrolytic capacitor comprising: acapacitor element that contains a sintered porous anode body thatincludes tantalum, a dielectric that overlies the anode body, and asolid electrolyte that overlies the dielectric; an anode lead extendingfrom a surface of the capacitor element; an anode termination that is inelectrical connection with the anode lead and a cathode termination thatis in electrical connection with the solid electrolyte; and a casingmaterial that encapsulates the capacitor element and anode lead, whereinthe casing material is formed from a curable resinous matrix that has acoefficient of thermal expansion of about 42 ppm/° C. or less at atemperature above the glass transition temperature of the resinousmatrix; wherein the capacitor exhibits an initial equivalence seriesresistance of about 200 mohms or less as determined at an operatingfrequency of 100 kHz and temperature of 23° C., and wherein the ratio ofthe equivalence series resistance of the capacitor after being exposedto a temperature of 125° C. for 560 hours to the initial equivalenceseries resistance of the capacitor is about 1.1 or less.
 2. The solidelectrolytic capacitor of claim 1, wherein the resinous matrix has acoefficient of thermal expansion of about 11 ppm/° C. or less at atemperature below the glass transition temperature of the resinousmatrix.
 3. The solid electrolytic capacitor of claim 1, wherein theresinous matrix has a glass transition temperature of from about 50° C.to about 180° C.
 4. The solid electrolytic capacitor of claim 1, whereinthe ratio of the equivalence series resistance of the capacitor afterbeing exposed to a temperature of 125° C. for 750 hours to the initialequivalence series resistance of the capacitor is about 2.0 or less. 5.The solid electrolytic capacitor of claim 1, wherein the ratio of theequivalence series resistance of the capacitor after being exposed to atemperature of 125° C. for 1,000 hours to the initial equivalence seriesresistance of the capacitor is about 2.0 or less.
 6. The solidelectrolytic capacitor of claim 1, wherein the ratio of the equivalenceseries resistance of the capacitor after being exposed to a temperatureof 125° C. for 1,250 hours to the initial equivalence series resistanceof the capacitor is about 2.0 or less.
 7. The solid electrolyticcapacitor of claim 1, wherein an interfacial coating covers at least aportion of the anode termination.
 8. The solid electrolytic capacitor ofclaim 7, wherein the interfacial coating also covers at least a portionof the anode lead.
 9. The solid electrolytic capacitor of claim 7,wherein the interfacial coating includes a fluoropolymer, siliconepolymer, organometallic compound, or a combination thereof.
 10. Thesolid electrolytic capacitor of claim 1, wherein the resinous matrixcontains a polycyanate containing at least two cyanate ester groups. 11.The solid electrolytic capacitor of claim 10, wherein the polycyanatecontains a polycyclic aliphatic radical containing two or more cyclicrings.
 12. The solid electrolytic capacitor of claim 11, wherein thepolycyclic aliphatic radical includes cyclopentadiene, norbornane,bornane, norbornadiene, trahydroindene, methyltetrahydroindene,dicyclopentadiene, bicyclo-(2,2,I)-hepta-2,5-diene,5-methylene-2-norbornene, 5-ethylidene-2-norbornene,5-propenyl-2-norbornene, 5-(4-cyclopentenyl)-2-norbornene,5-cyclohexylidene-2-norbornene, 5-vinyl-2-norbornene, or a combinationthereof.
 13. The solid electrolytic capacitor of claim 12, wherein thepolycyanate is a dicyclopentadiene bisphenol cyanate ester.
 14. Thesolid electrolytic capacitor of claim 1, wherein the resinous matrixcontains an epoxy resin.
 15. The solid electrolytic capacitor of claim14, wherein the epoxy resin is a phenolic novolac epoxy resin.
 16. Thesolid electrolytic capacitor of claim 15, wherein the phenolic novolacepoxy resin is a phenol-novolac epoxy resin, cresol-novolac epoxy resin,naphthol-novolac epoxy resin, naphthol-phenol co-condensation novolacepoxy resin, naphthol-cresol co-condensation novolac epoxy resin,brominated phenol-novolac epoxy resin, or a combination thereof.
 17. Thesolid electrolytic capacitor of claim 1, wherein the resinous matrixfurther includes an inorganic oxide filler in an amount from about 75wt. % to about 99.5 wt. % of the matrix.
 18. The solid electrolyticcapacitor of claim 17, wherein the inorganic oxide filler includessilica.
 19. The solid electrolytic capacitor of claim 1, wherein thecapacitor element further comprises a cathode coating that contains ametal particle layer that overlies the solid electrolyte, wherein themetal particle layer includes a plurality of conductive metal particles.20. The solid electrolytic capacitor of claim 19, wherein the metalparticles include silver.
 21. The solid electrolytic capacitor of claim1, wherein the solid electrolyte includes a conductive polymer.
 22. Thesolid electrolytic capacitor of claim 21, wherein the conductive polymerhas repeating units of the following formula:

wherein, R₇ is a linear or branched, C₁ to C₁₈ alkyl radical, C₅ to C₁₂cycloalkyl radical, C₆ to C₁₄ aryl radical, C₇ to C₁₈ aralkyl radical,or a combination thereof; and q is an integer from 0 to
 8. 23. The solidelectrolytic capacitor of claim 22, wherein the extrinsically conductivepolymer is poly(3,4-ethylenedioxythiophene) or a derivative thereof. 24.The solid electrolytic capacitor of claim 21, wherein the solidelectrolyte also contains a polymeric counterion.
 25. The solidelectrolytic capacitor of claim 1, further comprising an externalpolymer coating that overlies the solid electrolyte and containspre-polymerized conductive polymer particles and a cross-linking agent.